/**
 * 852. 山脉数组的峰顶索引
 */
class Solution6 {
    public int peakIndexInMountainArray(int[] arr) {
        int left = 0, right = arr.length - 1;

        while(left < right) {
            int mid = left + (right - left + 1) / 2;
            if(arr[mid] > arr[mid - 1]) {
                // 上升趋势
                left = mid;
            } else {
                // arr[mid] < arr[mid - 1]
                // 下降趋势
                right = mid - 1;
            }
        }

        return left;
    }
}